While Microsoft's latest Windows Phone 8 update is slowly rolling out to existing handsets, the company is prepping new changes that will be made available by the end of the year. Sources familiar with Microsoft's Windows Phone plans have revealed to The Verge that the software maker is currently testing a General Distribution 3 (GDR3) update. The update is designed for new hardware initially, and will provide a rotation lock feature, UI changes to Live Tiles, and a driving mode option that's designed for in-car use.